best answer left a few things out.. its been around since the 70's... so you can find a LOT of hippies going to the events.. basically what goes on there, is its an expression of ones self.... acid cannibis and other drgs are taken by most if not all and are shared throughout the community... people are dancing... people are naked... people are f*kd up! great event to go see... oh yeah and its because its a private community event out in the middle of the desert so police dont care.
Burning Man is an annual event held in the Black Rock Desert in northern Nevada, in the United States. The event starts on the Monday before, and ends on the day of, the American Labor Day holiday. It takes its name from the ritual burning of a large wooden effigy on Saturday evening. The event is described by many participants as an experiment in community, radical self-expression, and radical self-reliance. Basically, it's a giant festival where the burn a giant wooden man.
It looks like a very wild event, I would not browse for if you are at work. Here is the site.
I saw that in a Nicholas Cage movie. :)